High temperature conversion of heavy oils



B. 1. SMITH EI'AL HIGH TEMPERATURE CONVERSION OF HEAVY OILS Filed April13. 1.955

Sept. 22, 1959 s Sheefis-Sheet 1 I A P m 5 6 DDIIVERSIDII T0 DRY DAS,SDF/LB. DDKE'FREE FEED 9 u 5 4 5E mse i 232 :3 a 2: m

BROOK I. 5mm

INVENTDRS HAROLD W SCHEELINE EDWARD D. BDSTON B) K 5W ATTURNEY p 22,1959 B. l. SMITH EI'AL 2,905,629

HIGH TEMPERATURE CONVERSION OF HEAVY OILS Filed April 13. 1955 3Sheets-Sheet 2 5 Fla-2 4- I I l III I I l'l 0 I 2 3 4 5 6 7 8 9 ID I!CONVERSION T0 DRY OAS, SOF/LD. COKE-FREE FEED BROOK I. SNITH HAROLD NSOHEELINE INVENTORS EDWARD D. BOSTON BY- X. @W ATTORNEY Sept. 22, 1959B. l. SMITH ETAL 2,905,629

HIGH TEMPERATURE CONVERSION OF HEAVY OILS Filed April 15. 1955 3Sheets-Sheet 3 human mom/0r 53 Of as r0 mm ouEncn srmrm 27" I I 1 T W li 1: u 3 0mm smlrm womn moron 3! i g 45' II RESIOOH 45 O STEAM 0R mmFIG-3 BROOK I. SMITH HAROLD W. SOHEELINE INVENTORS EOWARO D. BOSTON BY,6 M ATTORNEY upon several factors.

HIGH TEMPERATURE CONVERSION OF HEAVY OILS Brook I. Smith and Harold W.Scheeline, Elizabeth, and Edward D. Boston, Westiield, N.J., assignorsto Esso Research and Engineering Company, a corporation of DelawareApplication April 13, 1955, Serial No. 501,018 Claims. (Cl. 208127) Thepresent invention relates to high temperature conversion of heavy oils,particularly of heavy residual oils such as reduced crude petroleum,coal tar bottoms and the like. The invention has particular utility inthe coking of heavy hydrocarbon oils to produce a relatively wide rangeof unsaturated hydrocarbon products, especially those of moderately lowmolecular weight. The unsaturated hydrocarbons of low molecular weightare widely used as starting materials for production of variouschemicals and polymers and the present invention is designed tofacilitate the production of these starting materials. At the same time,the invention has as a major object the economical production ofrelatively large yields of the lower aromatic hydrocarbons, such asbenzene, toluene, etc., within the gasoline boiling range, that is,below about 430 F., together with a group of C -C unsaturated materialscommonly known as resin-formers because of the ease with which they maybe polymerized to form resinous products of commercial utility. Thesematerials are useful not only as chemical raw materials and solvents butmost of them are in demand in large quantities and at premium prices formotor fuel ingredients where high quality is needed.

Conversion processes of this general type have been suggestedpreviously, eg in U.S. Patent No. 2,436,160 issued to Blanding.Reference may be had to this patent for general operating conditions. Itwill be understood,

however, that the present invention involves some new concepts andtechniques not disclosed by Blanding.

The economical conversion of heavy hydrocarbon oils to relatively lowmolecular Weight products such as C gases, C -C unsaturates, and loweraromatics depends Certain products of those just mentioned are producedin relatively large yields at particular operating conditions but at theexpense of other valuable products in the same list which could beproduced in larger or at least moderate quantities by varying theconditions slightly or to a reasonable degree. Factors such asconversion temperature, conversion severity (which is commonly afunction of conversion time), total pressures or partial pressures andthe like, are very important in controlling product distribution. Therequisite control cannot ordinarily be obtained by merely adjustingtemperatures or pressures.

According to the present invention, it has now been found that improvedconversion and superior economic yields of the more valuable of theproducts listed above may be obtained by integrating control of certainadditional factors into the coking process. Principal among these are(a) control of the extent of conversion to dry gases (C and lighter) and([2) control of the hydrocarbon partial pressure at the outlet of thereaction zone.

The preferred coking process is one which utilizes fluidized orsuspended heat carrying particles of a size range between about 5 and1500 microns, preferably 20 to 400 microns average diameter, theparticles being substantially inert catalytically. Other types ofconversion ,PI'OCCSSS such as steam cracking are affected to aconsiderable extent by the same control factors. To that extent, theinvention is applicable also to other types of thermal processes carriedout at very high temperatures. In general, the term high temperature, asused herein, refers to reaction zone temperatures of around 1200" F. orhigher.

High conversion of heavy oils, such as petroleum residua, to dry gas,i.e. C and lighter, can be accomplished by high temperature thermalcracking as is well known. By conversion to dry gas, it is meant todefine conversion to C and lighter hydrocarbons plus hydrogen, thequantity of gas of the products being expressed either as standard cubicfeet (s.c.f.) per pound of feed or as a percentage by weight of theoriginal feed, on a coke-free basis. The latter expression will be morefully explained hereinafter but, in general, coke-free feed means thetotal feed minus the amount eventually converted to dry coke. Hightemperature conversions of this type commonly result in good yields ofethylene, if the temperature is above 1200 F. With increasingtemperatures and conversion times production of ethylene goes up, alongwith other light gas products. It is not uncommon to secure dry gasyields of 40%, 50% or even more. Expressed another way, it is notunusual to produce 7, 8 or more s.c.f. ofv dry gases per pound of feed.However, one aspect of the present invention is the discovery thatmilder conversions than these are often more etficient and economical.High conversions result in substantial destruction of products having 4or more carbon atoms and these are frequently the most valuable of allthe materials produced. Moreover, the yields of low molecular weightmaterials such as hydrogen and methane and other prod nets of loweconomic value are fairly high.

On the other hand, at very high conversion temperatures, for examplel300 or higher, and especially above 1500 F., the yields of aromaticssuch as benzene increase rapidly with increasing temperatures but so doyields of acetylenes. Where butadiene is a desirable product, as itusually is, the production of C acetylenes in quantity is particularlyundesirable because of the very considerable difliculty of separatingthe latter from butadiene.

Hence, when it is desired to produce butadiene, isoprene, resin-formingmaterials in the C to C range and also benzene in a single economicalprocess, increased yields of any one of these are apt to be secured atthe expense of considerable losses of some of the others. The matter ofcontrolling conditions so as to get high yields, for example, ofbutadiene and C to C resin-formers while also obtaining reasonably goodyields of benzene and related aromatics involves considerabledifiiculty. The present invention and the experimental work upon whichit is based go a long way towards solving this difiiculty.

Ordinarily, the most desirable products to be obtained by hightemperature thermal cracking of heavy hydrocarbons are the C and Cdiolefins, such as butadiene,

isoprene, piperylene and cyclopentadiene. These are used in largequantities in the production of synthetic rubber and related polymersand copolymers. The next usually they are in the order listed. Thediolefins are usually produced in relatively small quantities. Attemptsto greatly increase their yields usually result in heavy sacrifices inyields of the other products, Hence one bject of the present inventionis to provide a balanced process wherein control is maintainedsimultaneously to afair degree of accuracy to achieve good yields of themost valuable products consistent with over-all yields of all productsthat improve economy of operation.

A more specific object of the present invention is the production ofnear maximum yields of the C and C diolefins and C to C resin-formers,accompanied with good yields of the Ca to 430 F. aromatics. The controlof these yields is accomplished, as noted above, by an intercontrol ofconversion temperature and time to control total dry gas production plusfurther control by the use of low hydrocarbon partial pressure at theproduct outlet. Specifically, it is found that control of the overallconversion to dry gas is highly important because the yields of the mostdesirable products, especially the diolefins and resin-formers varyconsiderably with this ratio. They also vary in a usually inverserelationship, and quite rapidly, with the hydrocarbon partial pressuremaintained in the reaction zone.

The invention will be more clearly understood by reference to theaccompanying drawings wherein Figure 1 is a graph showing the efiect ofdry gas conversion levels on total yields of C to C diolefins plus C -Cresiniormers;

Figure 2 is a graph showing the effect of dry gas conversion levels ontotal yields of Cg-C 'aromatics plus C 490 F. resin-formersj Figure 3shows diagrammatically a typical high temperature conversion systemsuitable for carrying out the process.

Referring now to Fig. 1, it will be noted that the graph shows a totalyield of C -C diolefins plus the C -C unsaturated predominantly linearand polymerizable hydrocarbons which are useful for making light coloredresins and are commonly called resin-formers. On the basis of coke-freefeed, by weight, this yield increases with increasing temperatures.Aside from this, however, at each temperature the total yield passesthrough a maximum at about the point where the dry gas (C yield isbetween 6 and 7 standard cubic feet per pound of cokefree feed. Theeffect of dry gas conversion level is very striking, and is quiteindependent of conversion temperature. At a given temperature, the lowerdry gas conversion level produces less C -C diolefins and more C -Cresin-formers than higher conversion levels. The total .of these,however, passes through a definite maximum. This is true although thetotal conversion-of feed to coke and to other gas and liquid products,respectively, is sub- .stantially unchanged. These data are clearlyindicated in Fig. 1 and are given in fuller detail in Table I. The feedemployed for these data was a South Louisiana residuum.

TABLE Effect of conversion level Run No 1 2 3 4 -Temp., F 1,260 1,250 1,260 1,268 110 part. press. p.s.l.a 8 8 6 5 Conversion to C: and li er gaV S e f./lb. feed 2. E9 4 60 5. 55 9.12 S c iJlb. coke-free fee 3.48 555 6. 70 11.0 Yields, weight percent on [e C4-C diolefins l. 5 4. 8 5.33. 4 CsC7 resin-formers 3. 4 2. 5 1. 9 1. 1 Other gas and liquid producs 78. 1 75. 7 75. 8 7& 5 Coke 17 17 17 17 Yields, weight percent oncoke-tree e Cr-Cs diolefins p (ls-C1 resin-formers. 5. 9 8.8 8. 7 5. 4

It is clear from Fig. 1 and from Table I that the optimum level of totalC -C diolefins and C C, resinformers is obtained by keeping the dry gasconversion level between about 4 and 8 s.c.f. per pound of feed on acoke-free basis.

The coke-free basis mentioned is determined originally by actualmeasurement of the weight of dry coke produced, this quantity beingdeducted from the weight of the feed. However, from a large mass of datawhich have been obtained it is now quite possible to compute cokefre'efeed byhnowing the carbon and hydrogen content of the feed stock and theConradson carbon residuenumber of the feed in weight percent.

Thus, where D=the coke deposit in weight percent of feed, obtained onconversion to lighter products and coke, it is found by experiments thatD also is equal numerically to the largest of the terms R, the Conradsoncarbon residue, 01 C1lH+5.8G where Cand H, respectively, are weightpercentages of carbon and hydrogen in the feed and G is s. c.f. of drygas produced for each pound of feed on coke-free basis.

Now, for optimum production P of C -C diolefins plus C -C resin-formers,the formula becomes where G, the cubic feet of dry gas .per pound ofcoke frec feed, is not less than 4 nor more than 8 or P43 "1+o.osso

whichever is the smaller.

The optimum range shifts only moderately when the most valuable productsare the C to C aromatics plus the broader and largely aromatic series ofunsaturated hydrocarbons ranging from C (isoprene, piperylene) 'to the490 F. boiling range, known generally as resin-formers, because theypolymerize readily. These hydrocarbons usually produce hard and darkcolored polymers. Yields are indicated graphically in Fig. 2 where themaxima are quite sharply defined. The total yields are higher at lowertemperature-just the reverse of the results in Fig. 1. However, themaxima '(total) are still within the range of about 5 .to 1.0 s.c.f. drygas per pound of coke-free feed.

The same general phenomena are observed on switching to other feedstocks. So long as the operating conditions are regulated to obtain drygas conversion within the preferred limits, the yields of the mostvaluable -products remain high.

Thus, as shown in Table II, when the conversion con ditions .wereregulated (by control of contact time) to keep the dry gas yieldconstant (on a coke-free feed basis) the yields of butadiene, Cdiolefins, and C8-C resin-formers remained quite constant.

TABLE II 'Efiect of feedstock Erampleu A -B Feedstock -Virgln gas 011.".

Temperature, F .l,

Hydrocarbon part. press, p.s.i.a

Conversion to C and lighter gas:

S.c.t.llb. teed S:c.f., lb. coke-free feed.--

Yifeltils, weight pereenton coke-free So. La. resld. 1,260. j

men

Total dry gas containing substantial portions of ethylene, propylene.methane,

Bntadlene (Jr-C resin-form Other 04/430 F gas conversion was 39.3% byweight for the residuum and 43.3% for the virgin gas oil. Still thetotal yields of butadiene, C diolefins and C -C resin-formers are nearlyidentical.

The formula for optimum production of C -C aromatics plus the largelyaromatic C 490 F. resin-formers is the same as that given above, i.e.the smaller of the expressions G(l0.01R) or (1--0.01C+0.1IH

but here G is preferably within the range of 6 to 10 rather than 4 to 8.The over-all range for all the products then lies between about 4 and 10s.c.f. of dry gas per pound of feed on coke-free basis. The latter basisis important.

' Turning now to consideration of the effect of hydrocarbon partialpressure, it will be noted in Table I that this amounted to 8 p.s.i.a.in the first two runs and 5 p.s.i.a. in the last two. In Table II,Examples A and B 'were both run at 5 p.s.i.a. (using steam to reduce thepartial pressure). For optimum production of C -C diolefins the lowerpartial pressures are preferred whereas higher pressures are suitablefor production of aromatics. The preferred operating conditions for thetwo general classes of products are compiled in Table HI.

TABLE III Preferred operating conditions 04-0: diolefins plus C-C7resinformers C-C aro- Primary product matlcs plus 05-490 F.

resin-formers Conversion to C5 and lighter gas, s.c.t./lb.

coke-free feedr.

Temperature. El...

E0 partial pressure, p.s.i.a..

From the foregoing, it is clear that control of the severity ofconversion, as measured by production of dry gas, is a major factor incontrol of the product distribution. In general, at higher severity theproduction of butadiene,

C diolefins, and C to C resin-formers drops off markedly. The productionof aromatics, including the broad C to 490 F. class of resin-formerswhich are largely aromatic, goes up rapidly as does the concentration ofsuch aromatics in the gasoline fraction. Ethylene production, whilehigher in absolute value, drops off in its ratio to total dry gas. Thesedata are compiled in Table IV.

TABLE IV High severity Normal severity Examnln O 1) Cu-Ct aromatics C-490 F. resin-formers Coke 24 Concentration of aromatics in (Ya-430 F.after removal of resin, weight percent 95 Concentration of ethylene inC2 and hter,

mol. percent 26 While the foregoing discussion has not been directed toany specific conversion process, the presently preferred process forapplication of the principles ofthe invention .will next be described insome detail.

Referring to Fig. 3, there is shown 'a hopper or ac cumulator 11 forfluidized and preheated solid particles of heat carrying material. Theseparticles are relatively and preferably substantially completelynon-catalytic. Hopper 11 is connected at the bottom to a transfer line13 into which a fluidizing and/or stripping gas may be introducedthrough inlet 15. The hot fluidized solids flow downward by gravity intothe transfer line. A suitable valve, not shown, may be provided tocontrol and/or shut off the flow when desired.

Transfer line 13 includes a reverse bend 17 and additional fluidizingand/or lifting gas may be introduced at inlets 19 and 21. As many inletsas are needed will be used, as is well understood in the art. Variablecontrols are desirable here, as indicated, to control steam supply andthereby control hydrocarbon partial pressure in the reactor.

The ascending leg of the transfer line, particularly the upper portionthereof, serves as the reactor vessel for the system as indicated at 25.The feed to be converted, typically a heavy petroleum residuum, issprayed, through a suitable nozzle system 27 into the ascending streamof hot solid particles. The feed is preferably preheated and is usuallyand preferably substantially in liquid form, but it may comprise solidparticles of pitch, bitumen, bituminous coal, etc. The fluidized orsuspended heat carrying particles contact the feed, which is in finelydivided form, and cause thermal conversion thereof. The temperature ofthese patricles is sufficiently high to maintain the desired reactiontemperature.

This temperature may be from as low as 1150 F. to as high as 1600 F. oreven higher. For optimum production of butadiene, C diolefins and the C-C resin formers a temperature below about 1350 F. is desirable,preferably between 1200 and 1300 F. Where the C -C aromatics and relatedproducts are more in demand, higher temperatures, desirably above 1300F. and preferably above 1350 F. are needed.

In any case, the fluidizing gas may be steam or light hydrocarbon gases.Where it is desirable to keep hydrocarbon partial pressure low, as it isparticularly for production of butadiene and related materials, steam orother non-hydrocarbon gas must be used in suitable proportions. Thesystem of Fig. 3 is quite operable at or near atmospheric pressures.However, it may be operated at elevated pressures, up to 50 p.s.i.g.,p.s.i.g. or even higher if desired. Pressure operation, of course,requires pressure control valves, etc., not shown.

The time of reaction betwen the feed and the hot solid particles inreactor 25 is quite short, preferably 0.05 to 1 second or so. This timedepends, of course, on the dimensions of the reactor and the velocityand dispersity of the solids passing through it. The severity ofconversion, e.g. to dry gas, depends on both the temvapors andcarbonaceous residue or coke. The latter is deposited upon theheat-carrying solids which are cooled somewhat.

The stream of solids, vapors, etc., emerging from the transfer linereactor 25 passes into a cyclone type separator 27 where a quenchingspray 28, e.g. of hydrocarbon oil such as the feed, is injected to coolthe vapors so as to partially quench further reaction. Here coolingshould be at least 50 F. to substantially inhibit further reaction. Thesolids are separated and passed downwardly through the cyclone solidsoutlet line 29 into a stripper 31. Steam or other inert fluid isintroduced into the bottom of stripper 31 through line 33 and thestripped gas or vapor products are removed through line 35 and taken toa suitable recovery system, not shown.

The partially quenched vapor products pass overhead "from separator 27through outlet line 37 where they may setters h gh r- .antodegradationof "theproducts. ,Qooling here should he at least 100 F. 'l'he coblantmay 'be 'w a'tr, rt hydrocarbons, or even a stream 'oifrelatively coolsolid particles, as is known in the art. Quenching at may sometimes besufficient but since it i nvo'lves (tooling the solids (which mustihereaftenbe'reheated as will be .eit plaine d) it is usually preferredtoq eseh only model- Tardy; a by cooling'50 is 100 n; at 28 and coolfurther, preferably at least 100 F and'usu ally tnrtlier at 39. Thequenched products ames tak'en to Iasuitable fractionator or otherrecovery apparatus, set shownf After stripping, the spent solids instripper 311 are taken through line '41 through a reverse bend into areheating er burning zone. Steam mother lifting or aerating gas )8introduced by means of line 43;. The heatingo'rburiiing'z'one'isina'tr'ansfer line burner 45 havin'g an alr inlet 47 at the bottomthereof. Additional inlets, not .shoyvn, may he provided if desired.'Within the heater or burner 45, the solids are usually reheated totliedesired temperature by combustion of pan, or all of the carbonaceoussolids deposited thereon .in the reactor. If desired, however, acombustible fuel "rich as gas or torch oil, may be introduced'with theair tosupply part or all of the heat required. The hot solids, with thegases of combustion pass upwardly'into 'a separator or cyclone 51 from'which the flue gases pass overhead. The separated solids passdownwardly into hopper 11 from whence the cycle is repeatedcontinuously. i i 7 While various solids, such as sand, mullitecorborun- 'du'm, metallic particles and the like may be used, petroleumcoke itself, as produced in the process is commonly pre'ferred becauseofits ready availability. Commonly, 'r'no're coke is produced than isneeded for combustion to supply the heat requirements. Hence 'thesurplus may be withdrawn, e.g. through line 57 under control of valve 59for other uses.

The hydrocarbon partial pressure in the reaction zone may be reduced byincreasing the steam fe'edfthrough lines 19, 21. As previouslyindicated, for C -C diolefins,

the partial pressure should be below 1 2 p.s.i.a. and preferably below10, 5 to 8 p.s.i.a. beinga preferred range. For other products it may behigher,e.g.' up to 20 p.s.i.a or more. Likewise, the velocity of thesolids, the degree of their dispersion, and the contact time beforequenching may be controlled by the steam feed rate. The temperature ofthe solid particles and their circulation rate may be controlled by theamount of air admitted "at 47. Various other controls will suggestthemselves and both the apparatus and the processmay be modified andvaried as will be obvious to those skilled in the art. The solidparticles employed, preferably coke, should be of fluidizable size, butmay vary from very fine, e.g. 10 microns to rather coarse, e.g. up to800 microns or more average diameter, the preferred range being "to 400.

In summary, the process of this invention involves the conversion ofheavy hydrocarbon or hydrocarbonaceous materials to low boilingmaterials, with selective control over the products, achieved by (a)controlling the severity of conversion by surveillance of dry gasproduction to hold it between about 4 and 10 s.c.f. per'poundof feedwhile (b) controlling the hydrocarbon partial pressure within thereaction zone. The controls needed are further determined byascertaining the Conradson carbon number of the feed and the percentageofcarbon and hydrogen therein, then applying the forrnu'las'enumeratedabove. .A shift from optimum production of C -C diolefins plus C -Cresin-formers (for light colored resins) to primarily aromatic materials(plus ethylene and some acetylenes and including resin-formers for darkcolored resins) involves merely a shift of conditions to raise the dryvgas production to the alternative optimum range. Bycontrollinghydrocarbon partial pressure, further control over theprocess is obtained.

jvaried considerably.

obvious variat n may be pract c d. w h n he stops at th T' s satiP a tis hea d to 9 r i s is: fa as the prior artfvvi ll permit. Thepreliminary quenching, by 50 F; or more, rnay be made more complete if ds t e i na e se ond uen hin i sw a r. but both steps are usuallydesirable, The size vwell ract Of h re sh mi e s he e d may be What isclaimed is: V

1. The process of converting'heavy hydrocarbonaceous materials to lowboiling normally vaporous or liquid hydrocarbons and solid carbonaceousresidue which com prises feeding a stream of said materials in finelydivided f rm n o con a w th a diz d o subs a t ally non-ca aly i h t aryi r d' par i at c b nacefiils residue produced iuithe process, at areaction temperature-of at least 1150 F. for a time sufficient to causeconversion of the feed to at least 4 and not more than a ou 1Qs-ci-dntsas (63) p r pou d. f ca eic w le upp y n n h ncn-hydw bq s toth reaction zone to keep hydrocarbon partial pressure be low about 20p.s.i.a. to thereby obtain substantially optimum economic yields of, (lC diolefins, C -C resinformers and lower aromatics, substantiallyirrespective of the quality of the feed. i V r.

v 2. The process of obtaining high yields of. diolefins and o r unsatrates from eavy. hydro on i1,. hi comprises feeding-saidoil in finelysubdivided particles into contact with a mobile mass of finely dividedheat carrying solid particles capable of being suspended in a gasiformstream, said particlesbeing preheated sutficiently to keep the reactiontemperature above 1150 -F., maintaining said, contact for a sutiicientlength of time to convert substantially all said feed to vapors andcarbonaceous residue while controlling the severity of conversion so asto keep dry gas production at a level between 4 and 8 s.c.f. per poundof coke-free feed mantaining hydrocarbon partial pressure below about1.2 p.s.i.a., passing a stream of the vapor and gas products. includingen trained solids out of the reaction zone, quenching the stream byinjecting sufficient coolant to, lower its tenr perature by. at least 50F., and separating the solids from the vapor and gas products. 7

3. The process of converting heavy petroleum residua o co nd apors of hco om c alu h ch s mprises preheating a supply of finely divided solidparticles of average diameter within the approximate range of. 20

.to 400 microns to a 'temperatureabove '1;l5 0 E, .passing a stream ofsaid particles by means ofa suspending gas through an extended reactionzone, feeding finely diyided petroleum residue, substantially in liquidphase, irito said zone to contact said particles, maintaining a contacttime from about 0.05 to about 1 second at a temper ature above l'150 F.,so controlled as to cause production of about 6 to 8 s.c.f. of dry gas(C per pound of coke-free feed, thereby also producing other vapors andcarbonaceous sidue pa s n the sa eshvapc rasd su pended particles out ofsaid reaction zone, separating ng steam at a dilue 4 was as r theparticles. 5. A process for producing high yields of desired bydrocarbonchemicals, whichcomprises-feeding a heavy hydrocarbon oil into a mass ofhot inert solids maintained in reaction "zone at a temperature abovell5i) F cone n id h d s bsa 9 b svn t i s e level 9 conversion at aconversionfle've l of between 4 10 set. of dry gas (C 1- per' poundofYcolte-free feed, a

reaction time in the range of 0.05 to 1.0 second being employed andnon-hydrocarbon gas being supplied to said reaction zone to maintain ahydrocarbon partial pressure of less than 20 p.s.i.a. within saidreaction zone,

thereby producing optimum economic yields of C -C 5 2,698,672

diolefins, C -C resin-formers and lower aromatics.

References Cited in the file of this patent UNITED STATES PATENTS2,426,160 Blanding Feb. 17, 1948 Burnside et al. Ian. 4, 1955 2,731,508Iahnig et a1. Jan. 17, 1956

5. A PROCESS FOR PRODUCING HIGH YIELDS OF DESIRED HYDROCARBON CHEMICALS,WHICH COMPRISES FEEDING A HEAVY HYDROCARBON OIL INTO A MASS OF HOT INERTSOLIDS MAINTAINED IN A REACTION ZONE AT A TEMPERATURE ABOVE 1150*F.,CONVERTING SAID HYDROCARBON OIL BY CONTROLLING THE LEVEL OF CONVERSIONAT A CONVERSION LEVEL OF BETWEEN 4 AND 10 S.C.F. OF DRY GAS(C3-) PERPOUND OF COKE-FREE FEED, A REACTION TIME IN THE RANGE OF 0.05 TO 1.0SECOND BEING EMPLOYED AND NON-HYDROCARBON GAS BEING SUPPLIED TO SAIDREACTION ZONE TO MAINTAIN A HYDROCARBON PARTIAL PRESSURE OF LESSS THAN20 P.S.I.A. WITHIN SAID REACTION ZONE, THEREBY PRODUCING OPTIMUMECONOMIC YIELDS OF C4-C5 DIOLEFINS, C6-C7 RESIN-FORMERS AND LOWERAROMATICS.